1. Field of the Invention
The present invention relates to a variable compression ratio engine apparatus and method for an internal combustion engine (or, simply “engine”, herebelow).
2. Description of Related Art
Conventional known engines include those of the type for use with vehicles capable of using, as an alternative fuel to gasoline fuel, ethanol blended gasoline (“alcohol fuel”, hereinbelow), which is a blend of gasoline and ethanol. Such a vehicle is called “FFV” (i.e. flexible fuel vehicle), and an engine for the vehicle is called “FFV engine.”
Alcohol fuel is referred to as an “E85 fuel (ethanol content: 85%)” corresponding to the ethanol content. While fuel containing only gasoline, without any ethanol, is sometimes referred to as “E0 fuel”, “alcohol fuel” herebelow will refer to the ethanol blended fuel, inclusive of an ethanol-100% fuel, and “gasoline fuel” herebelow will refer to “gasoline-100% fuel” not containing ethanol.
Alcohol fuel has a higher octane number than gasoline fuel and is therefore less likely to cause knocking, so that the FFV engine can be operated at a high compression ratio. As such, in the FFV engine, alcohol fuel can be combusted at high temperature, increasing the thermal efficiency and reducing NOx emission.
In the case of the conventional FFV engine, even in the event of operation using alcohol fuel, the operation has to be performed at a low compression ratio corresponding to gasoline fuel in order to prevent knocking that occurs during operation with gasoline fuel.
In a known engine permitting variable compression ratio control, a piston and a crankshaft are coupled together by way of a plurality of links, and a control link is controlled by an actuator mounted to a cylinder block of the engine, whereby the piston stroke is varied to vary the compression ratio. According to the variable compression ratio engine, even in the case where fuels, such as alcohol and gasoline fuels having different octane numbers, are used, the compression ratio of the engine can be controlled corresponding to the used fuel.
Nevertheless, however, problems remain in that, when the compression ratio is changed during operation involving combustion, the actuator has to be driven against loads generated with combustion pressure or the like, so that a large actuator has to be used for a correspondingly large drive force, which increases the costs.
The present invention has been made by drawing attention on these problems, and an object of the invention is to provide a variable compression ratio control apparatus and method for an engine, that are capable of performing variable compression ratio control and that enable compactness of an actuator.